1. Field of the Invention
The present invention relates generally to a Visible Light Communication (VLC) system, and more particularly, to a method and apparatus for generating a visible signal to enable a user to confirm the amount of data transmission while receiving data.
2. Description of the Related Art
VLC refers to a wireless communication technique using light within a visible light wavelength region. Recently, with the spread of Light Emitting Diodes (LEDs), extensive research is being conducted into VLC technologies. In the general VLC system, a transmitter sends visible light using an LED or a Laser Diode (LD) as a light source and a receiver processes the visible light using a Photo Detector (PD) etc. Infrared communications use similar techniques to those of a VLC system. FIG. 1 is a flow chart illustrating a data transmission process in a general wireless communication system using infrared rays. As illustrated in FIG. 1, wireless communication using infrared rays includes an infrared communication activation process 101, an external infrared communication device search process 102, a communication scheme determination process 103, a connection process 104, a data transmission process 105, a connection release determination process 106, and a communication connection release process 107. Through such a series of processes, a user arranges a communication link by directing light to an infrared communication device.
A data transmission scheme between a transmitter and a receiver that perform infrared communication is described with reference to FIG. 2. FIG. 2 is a diagram illustrating a data transmission scheme in a data link layer of an infrared wireless communication system. A transmitter 201 transmits data to a receiver 202 in step 203. If the data is successfully received, the receiver 202 transmits an ACKnowledgement (ACK) signal as a response to the reception of the data in step 204. In this way, data transmission is performed between the transmitter 201 and the receiver 202. However, since a user cannot directly confirm a communication state or communication channel state between devices, even though a link is disconnected in the middle of transmitting data between communication devices after the communication link is established, the user has no way of knowing the status of the communication link state.
VLC which is being currently developed is different from infrared communication in that it considers such a problem. Namely, the most distinctive feature of VLC contrasted with infrared communication is that VLC enables a user to be able to directly confirm a link state by using a light source of a visible light band. Therefore, a user can control the direction of a light signal so that light is directed to a target device even in the process of forming the communication link.
Since infrared communication uses wavelengths of the invisible light band, a communication link is invisible to a user and therefore a user cannot know a situation in which communication is performed. However, VLC uses a light source of a visible light band so that a user can visually confirm a communication channel state. In a communication scheme using visible light as a light medium, there is a need for methods using visible light in various ways and, in this case, the convenience of a user should be first considered. For example, if a user can intuitively know a transmission degree of data, that is, the transmission amount or transmission ratio of data while data is transmitted and received, the convenience of a user will increase.